Circuit shell enclosure

ABSTRACT

An enclosure for a circuit on a printed circuit board consisting of two boxes fastened to the opposite sides of the printed circuit board. The boxes each have one open side which faces the printed circuit board and seals against it by means of a gasket, creating protected areas under the boxes on both sides of the printed circuit board. The boxes are offset so that protected areas on one side of the board are directly opposite both protected and unprotected areas on the other side of the board. This allows the top sides of connectors, terminals, and feed-through fittings installed on the board to be unprotected and accessible, while their solder sides are protected as are all components of the circuit and interconnecting wiring on both sides of the board.

CROSS REFERENCE TO TO RELATED APPLICATIONS

[0001] Not Applicable

FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

[0002] Not Applicable

MICROFICHE APPENDIX

[0003] Not Applicable

BACKGROUND OF THE INVENTION

[0004] This invention relates to enclosures, specifically for printed circuit boards.

[0005] Circuits on printed circuit boards often need to be enclosed to prevent physical damage, to keep out dust and moisture, and to eliminate electric shock and short circuit hazards. The prior art in enclosures for printed circuit boards consists of a large variety of metal and plastic boxes designed to totally contain the printed circuit board. Wires, cables, and pressure/vacuum tubing attached to the printed circuit board must first pass through the walls of the enclosure by means of feed-through fittings, compression fittings, or connectors. This type of enclosure for printed circuit boards has the following deficiencies:

[0006] (a) Penetration of the enclosure by the wiring harness is a design problem requiring significant engineering effort.

[0007] (b) Connectors and compression fittings installed on the enclosure, and the labor to install them, add significantly to the cost of the enclosure.

[0008] (c) Compression fittings are designed for the round cross-section of cables or tubing and cannot seal effectively around a group of individual wires.

[0009] (d) Connectors on the enclosure are redundant when connectors are also located on the printed circuit board.

[0010] (e) Cables and tubing are not separable from the compression or feed-through fittings and enclosure once the end connectors are attached. Wires are not separable from the enclosure once soldered to connectors mounted on the enclosure. The enclosure consequently becomes part of the wiring harness and cannot be replaced or moved without considerable effort.

[0011] (f) Removing the lid of the enclosure allows only very restricted access to the card for test, modification, or repair.

[0012] (g) The enclosure must be oversized to contain relief bends in cables and tubing, to provide working room for attaching terminals and connectors, and to contain extra cable or tubing for slack if the card is to be removed from the enclosure while operating for access during test, modification, or repair.

[0013] There is a need for an improved enclosure that protects the circuits on a printed circuit board without the above deficiencies.

BRIEF SUMMARY OF THE INVENTION

[0014] Accordingly, the advantages of the Circuit Shell Enclosure are that the above mentioned prior art deficiencies are eliminated as follows:

[0015] (a) There is no penetration of the enclosure by the wiring harness, so no engineering effort is required in that regard.

[0016] (b) No feed-through fittings, compression fittings, or connectors are needed on the enclosure so the expense of those devices and the labor to install them is eliminated. Pressure/vacuum tubing, cable, and wires are run directly to fittings and connectors on the printed circuit board.

[0017] (c) Individual wires pose no special sealing problem and, like cable, can be run straight to terminals or connectors on the printed circuit board without first going through the enclosure.

[0018] (d) There are no connectors on the enclosure redundant to the connectors on the printed circuit board.

[0019] (e) The enclosure stays completely separate from the wiring harness and can be removed or replaced without disturbing the wiring.

[0020] (f) The enclosure is easily removed without disturbing the wiring to give access to both sides of the operating printed circuit board for test, modification, or repair.

[0021] (g) The enclosure needs to be no larger than the printed circuit board since no working room is needed inside the enclosure for installing connectors, nor is room needed inside the enclosure to contain extra cable for relief bends or slack to allow removal of the board from the enclosure

[0022] The Circuit Shell Enclosure thus provides complete protection of circuits on a printed circuit board but does not restrict, enclose, or complicate external wiring connections to the board. Indeed the external wiring is greatly simplified because there are no redundant connections or feed through fittings in the walls of the enclosure. The Circuit Shell Enclosure is completely independent of the wiring and easily removed to gain unrestricted access to the operating board for test, modification, and repair. No enclosed coils of wire or cable are needed to provide slack for removing the printed circuit board from the enclosure. The inexpensive and easy to manufacture Circuit Shell Enclosure is compatible with all types of standard printed circuit board mounted connectors and terminals.

[0023] The following description illustrates an embodiment of the circuit shell enclosure but should not be construed as limiting the scope of the invention as determined by the appended claims.

DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

[0024] In the drawings FIGS. 1A and 1B show perspective and elevation views of the two boxes comprising the Circuit Shell Enclosure attached to opposite sides of a printed circuit board.

[0025]FIGS. 2A and 2B show the bottom view and cross section of one of the boxes.

[0026]FIGS. 3A and 3B show a typical circuit board designed for the Circuit Shell Enclosure, and a cross section of the circuit board with the two boxes of the Circuit Shell Enclosure installed along with a typical circuit component, connector, and feed through.

DETAILED DESCRIPTION OF THE INVENTION

[0027] A typical embodiment of the present invention is shown in FIGS. 1A and 1B which are perspective and elevation views of a printed circuit board with the two boxes of the circuit shell enclosure attached to the top and bottom of the board. Although not required to be so constructed, the boxes in this embodiment are identical to reduce the number of parts, and are made of plastic by injection molding. In this embodiment the printed circuit board is 6 inches square and the boxes are 4.5 inches wide by 6 inches long by 1.3 inches deep. The boxes are fastened to opposite sides of the board with their long dimensions perpendicular to achieve the desired result of having the protected area on one side of the board opposite both protected and unprotected areas on the other side of the board. The boxes each have one open side which faces the printed circuit board and seals against the board by means of a perimeter gasket which in this embodiment is an o-ring. FIG. 2A shows the bottom of a box with a groove 11 to contain the o-ring, and four box mounting holes 12 outside the area enclosed by the o-ring. In this embodiment the mounting holes are sized to accept #4 self-threading screws for fastening to the printed circuit board. Metal inserts or machine screws with nuts could alternatively be used in applications where the boxes must be frequently removed. FIG. 2B shows the cross section of a box and the groove 11 to contain the o-ring. When the boxes are fastened to the printed circuit board areas of the printed circuit board underneath the boxes and any contained components and interconnections are protected. FIG. 3A shows a bottom view of a printed circuit board laid out to accommodate the boxes and a simple example circuit. Although not necessary, printed circuit traces have been laid out where the o-rings of the top and bottom boxes contact the printed circuit board, with the trace on the top of the board being shown in dashed lines. To achieve a flat surface where the o-ring contacts the board it is desirable that either a continuous printed circuit trace as in this embodiment, or no traces at all be located underneath the o-ring. Screws are inserted into the holes 12 in the board and threaded into the four mounting holes in the corners of the boxes. With the boxes attached the corners of the board remain unprotected on both sides and have four board mounting holes 13 for attaching the board and enclosure assembly to a surface by means of brackets or stand-off posts.

[0028] In FIG. 3A when the two boxes are in place there will be a central area 6 protected on both sides of the board. Areas 4A and 4B will be protected only on the top side of the board. Areas 5A and 5B will be protected only on the bottom side of the board. FIG. 3B shows a cross section of the printed circuit board with the boxes attached and with the typical circuit component, connector, and feed through fitting installed. The circuit component in this example is a pressure sensor 7 which requires both electrical and physical connection to the outside of the enclosure. The electrical connection is accomplished by printed circuit traces on the bottom side of the board connecting pins of the pressure sensor with the solder side of a connector 8 soldered into holes in the board in area 5B. The physical connection of the pressure sensor is accomplished by plastic tubing 10 which connects the port of the pressure sensor to a feed through fitting 9 which has been soldered into a hole in the board in area 5A. This example illustrates how the Circuit Shell Enclosure protects both sides of a circuit board where there are components and interconnections between components, and also protects the side of the circuit board where wires, traces, and tubing are run from components to the solder side of connectors and feed through fittings. Although areas 4A and 4B are not used in this simple example, it can be seen that additional connectors could be installed in those areas on the bottom side of the board having their solder sides on the top side of the board in protected areas. When there are holes in the printed circuit board for connectors but connectors are not installed, such as on a prototype board, the unused holes can be filled with solder to maintain the water and dust proof integrity of the protected areas. The protected areas available for circuits and connectors are controlled by the size of the board and boxes. Additional circuit area could be gained by stand-off boards mounted to the main board in the areas underneath the boxes. All printed circuit board mounted connectors and terminals are compatible with the circuit shell enclosure. Single wires, flat and round cables, co-axial cables, fiber-optic cables, and pressure/vacuum tubing can all be accommodated using standard connectors and fittings. Universal printed circuit boards could be designed for the Circuit Shell Enclosure with circuit solder pad arrays and a variety of connector footprints for prototype use. Downloadable outlines of printed circuit boards compatible with the Circuit Shell Enclosure could be made available as templates for customers desiring to lay out custom printed circuit boards. 

What is claimed is:
 1. An enclosure for a circuit on a printed circuit board, comprised of two boxes, said boxes being attached to opposite sides of said printed circuit board by fastening means, said boxes each having one open side facing said printed circuit board, said open side of each said box having a perimeter gasket means for sealing against said printed circuit board resulting in a protected area on both sides of said printed circuit board underneath said boxes, such that at least one of said protected areas is opposite both protected and unprotected areas on the other side of said printed circuit board. 